Compiling Physicochemical Characteristics of Water Quality Monitoring Sites (Environmental Reference Points) in Japanese Rivers and Site Grouping

Abstract

In this study, we gathered the information on catchment area, elevation, land uses in the catchment area and within a 3 km buffer area, and five water quality parameters, including, i.e., pH (minimum) , biochemical oxygen demand, suspended solids, total phosphorus, and total nitrogen, for 2925 water quality monitoring (WQM) sites (environmental reference points) in rivers throughout Japan. The hierarchical cluster analysis was supplementarily performed using physicochemical characteristics to classify the WQM sites into the following four groups: Group 1 (986 sites) was characterized by the predominant forest land use in the catchment area and relatively good water quality. Groups 3 and 4 (345 and 310 sites, respectively) were characterized by predominantly paddy and dry fields, and urban land uses, respectively, and relatively poor water quality. Group 2 (1284 sites) had intermediate features between Group 1 and Groups 3 and 4. Thus, we developed the database of physicochemical characteristics for WQM sites in Japan to readily examine, for example, the features of WQM sites contaminated with a given chemical substance.